The present invention relates to a head for pumps in particular of the membrane or piston type and to a method for its manufacture, the pump being destined for use with fluids in general and, specifically, for watering and weeding.
The pumped liquid is thus generally constituted by an aqueous solution, made aggressive both by the presence of inorganic and organic electrolytes, and by the presence of solid substances in suspension, for instance crystalline substances, or inert sands.
The head is the main and most stressed component of a membrane or piston pump for fluids and must be such as to withstand chemically all pumped fluids, and mechanically the pulsating pressure due to the alternation of intake and delivery.
To meet such requirements, heads obtained with different manufacturing technologies are known.
In particular, known heads are made of brass by press forging, or of bronze by casting, or of aluminum by press forging or casting and possibly with superficial protection for instance through superficial anodizing, or through superficial coating made of thermoplastic material (plasticizing), or through spray painting.
Aluminum alloy heads have poor chemical resistance to the pumped products, especially weed killers and pesticides. Even superficial coatings constituted by a plastic film do not provide the necessary assurance both in terms of duration and actual efficiency, since such coatings peel off with use, are permeable to liquids by porosity, and are difficult to manage and control in terms of quality.
Cast or press forged heads made of copper alloys (bronze and brass) not only have poor chemical resistance but also high manufacturing costs.
Also known are heads made of thermoplastic resins, possibly with metal inserts in the fastening and anchoring points (threaded bushings). In this case, the problem of chemical resistance is solved but the heads thus obtained have insufficient mechanical and structural resistance; even the provision of metal inserts fails to solve the problem of the warping of the structure under the action of pressure and screw tightening.
The particular cyclical mechanical stress whereto the head is subjected causes the onset of fatigue yielding in the thermoplastic material, thus limiting the working life of the piece.
Heads made of cast iron by casting or of stainless steel by casting or press forging not only have low chemical resistance, but are also difficult to manufacture.
The aim of the present invention is to eliminate the aforesaid drawbacks and to make available a head for alternating pumps with high chemical and mechanical resistance, with the possibility of using the aforesaid invention for pumps with higher pressures, used in industries such as the chemical, agriculture and food production, plant husbandry, for acids and liquefied gases.
Said aims are fully achieved by the head for pumps in particular of the membrane or piston type and method for its manufacture, constituting the subject of the present invention, which is characterized by the contents of the claims set out below.
In particular the aforesaid head comprises a frame able to provide mechanical strength, integrated in a structure made of a material able to withstand the pumped liquids chemically. The head is obtained by means of a method characterized in that it comprises the positioning of the frame on appropriate references inside a moldbefore injecting thermoplastic material constituting the exterior structure of the head.